1. Technical Field
This invention relates to the art of electroplating, and more particularly to electrodepositing precisely uniform anticorrosive coatings onto flux permeable housings for subminiature electromagnetic metering devices.
2. Discussion of the Prior Art
Commercial mass electroplating of precision and nonprecision parts has heretofore been carried out by essentially two techniques: stationary rack electroplating, and rotating barrel electroplating. Stational rack plating involves immersion of conductive articles, supported on a cathodically connected rack into an electrolyte in which is also immersed sacrificial anodes spaced from the rack. The rack is held stationary within the electrolyte in a preferred orientation to the directionality of the galvanic field. Absolute uniformity of coating throughout all of the parts is extremely difficult if not impossible in this type of plating because of the directionality of the galvanic field and the presence of surfaces hidden from the galvanic field. Thus, stationary rack plating is unsuited to the deposit of precisely uniform coatings throughout the interior as well as exterior of subminiature articles, such as automotive fuel injector devices.
Barrel plating is generally used for goods that are too small for racking or for economical bulk plating of large volumes of parts (even variably sized parts). Unfortunately, barrel plating inherently requires tumbling of the goods within the barrel to obtain reorientation of each part with respect to the direction of the galvanic field. This tumbling action inhibits attaining an absolutly uniform, microthin coating throughout the plated surfaces of small parts because the impact of one good against the other will lead to void spots or damage to the goods by tumbling impact (see U.S. Pat. Nos. 4,696,728 and 4,671,862). Such impact should be distinguished from sliding motion, the importance of which will become apparent later in the description of this inventive application. Impacting is the exchange of forces at an angle to the surface contacted, whereas sliding is a contact generally parallel to the surface being contacted and involves forces far less than impacting.
What is needed is a method and apparatus that will allow large quantities of hollow precision parts to be electroplated with virtual perfect uniformity in microthin thicknesses (i.e., 0.0003-0.0005 inches) internally as well as externally. To achieve such goal, the method must create a flow reversal of the electrolyte during the plating cycle with respect to the article plated and must generate a variable path for the article being coated so that each experiences nearness and remoteness from the sacrificial anodes during plating.